The invention relates to that aspect of ophthalmological surgery which is concerned with operations upon the external surface of the cornea.
Operations of the character indicated include corneal transplants and keratotomies; such operations have traditionally required skilled manipulation of a cutting instrument. But, however keen the cutting edge, the mere entry of the edge into the surface of the cornea necessarily means a wedge-like lateral pressure against body cells displaced by the entry, on both sides of the entry. Such lateral pressure is damaging to several layers of cells on both sides of the entry, to the extent impairing the ability of the wound to heal, and resulting in the formation of scar tissue.
My original patent application Ser. No. 552,983, filed Nov. 17, 1983, includes a background discussion of the effects of various available wavelengths of laser radiation in ophthalmologic surgery and, in particular, surgery performed on the anterior surface of the cornea. It is explained that radiation at ultraviolet wavelengths is desirable by reason of its high photon energy. This energy is greatly effective on impact with tissue, in that molecules of tissue are decomposed on photon impact, resulting in tissue ablation by photodecomposition. Molecules at the irradiated surface are broken into smaller volatile fragments without heating the remaining substrate; the mechanism of the ablation is photochemical, i.e., the direct breaking of intra-molecular bonds. Photothermal and/or photocoagulation effects are neither characteristic nor observable in ablations at ultraviolet wavelengths, and cell damage adjacent the photodecomposed ablation is insignificant. The order of magnitude of this ablative process, in the case of radiation exposure at ultraviolet wavelengths (in the range of about 400 nm or less), is that an energy density of 1 joule/cm.sup.2 incises to a depth of 1 micron (1.mu.). Said original patent application discloses a technique of scanning a laser beam over the anterior surface of a cornea in such a controlled pattern as to sculpture said surface, imparting a new curvature to said surface, whereby to achieve optical correction of an optically deficient eye. But the scanner and scanner control to perform the technique are relatively complex and expensive.